The present invention is generally directed to a novel microporous solid that can be effectively used in catalytic applications, such as in automotive exhaust treatment. More particularly, the present invention is directed to a microporous composition that is constructed by employing a salt template which can be readily removed without destroying the framework of the micropore. Further, depending upon the templating salt used and the concentration of the salt, various microporous solids can be formed having different geometric structures.
In the U.S. chemical industry, catalysts are used in over 90% of the manufacturing processes, transforming raw chemical ingredients into petroleum products, synthetic rubber and plastics, food products, chemicals, and pharmaceuticals, as well as controlling vehicle and industry emissions. Catalytic processes are involved in nearly 20% (approximately $1 trillion) of the U.S. gross domestic product and associated jobs. In economic terms, the U.S. chemical industry produces over 7,000 different products worth an estimated $375 billion per year, and generates 10% of the nation""s total exports. Worldwide, the manufacture of catalysts themselves, which come in forms as disparate as biological enzymes (specialized proteins) to fine metal powders to complex inorganic compounds like zeolites, is a $10 billion industry. The chemical industry, which is highly dependent upon catalysis, has the greatest trade surplus of all U.S. industries.
However, both chemical and refining industries have lost market share in recent years. New catalyst technologies are required to develop cleaner, safer, more energy-efficient, and lower cost processes because most existing processes were conceived when energy use and pollution minimization were less important than today.
Microporous solids have been explored as one possible material for such catalytic applications (also useful in other related applications, such as sorbent and molecular sieves applications). Microporous solids comprise a fascinating class of materials with most of their interesting properties resulting from the fact that the frameworks facilitate a structurally confined space on the order of small molecules. These spaces consist of micropore structures that can be used as a microreactor allowing for selective and controlled chemical processes.
Zeolites and zeolite-type materials, for instance, are well known for their practical importance in industrial processes, such as gas separation, catalysis, and shape-selective synthesis. The naturally occurring and synthetic microporous solids, including aluminosilicates, aluminophosphates, substituted alumino-phosphates, and zinco- (or beryllo-) phosphates or arsenates, are closed-shell, diamagnetic solids.
Significant progress in the synthesis of transition-metal-containing zeolite analogues has recently occurred, mainly because of the potential importance of these materials in industrial catalysis. In particular, a great deal of research activity has occurred relating to the use of organic and inorganic templates to direct the synthesis of zeolite-type, micro- and mesoporous materials. The open-framework solids developed from such research activity conceivably possess some unique chemical properties that are derived from enhanced catalytic activity (e.g. redox chemistry with respect to the anchored transition metal center) combined with shape-selective absorptivities, as compared to the Si- and Al-based materials.
However, in these transition-metal-containing zeolite analogues, low temperatures have typically been employed during synthesis, in part, to avoid the formation of condensed frameworks. Due to such low temperatures, the templating agents used cannot be readily removed from the structure by heating without destroying the framework of micropores. Specifically, because organic or organometallic templating molecules are often bonded strongly, such as via a covalent bond, to the microporous frameworks, the framework may collapse as the templating molecule is removed. As such, the effectiveness of such materials in novel applications is thereby diminished.
Therefore, a need currently exists for a class of new cost-effective catalysts that improve the yields of products, cheapen or simplify processes, open up attractive products previously too costly to market, and/or reduce the amount of pollution. In particular, the need exists for a class of microporous solids that allow removal of the space-filling, charge-compensation molecules without disrupting the overall microporous framework.
The present invention is directed to the design, synthesis, evaluation, and modeling of new and improved catalytic materials that will better meet the needs of tomorrow""s environmental and biochemical industries. The invention encompasses salt-templated microporous phosphate, arsenate, germanate and silcate analogs of zeolites. These newly discovered microporous solids exhibit superior structural, chemical, and physical properties compared to existing zeolite-based catalysts. In the proposed materials, the active sites and structures necessary for redox catalysis, for example, are included as part of the framework to facilitate easy separation and efficient recycling during the catalytic process. Further, a combinatorial approach along with the convention high-temperature, and/or high-pressure solid-state methods can be employed for properly fine-tuning the composition.
The new materials are potentially important for application in automotive exhaust treatment for pollution abatement, for removal of contaminates from alkaline solutions, for immobilization of halide salt radioactive waste, and for other various applications.
Microporous solids made according to the present invention can, in one embodiment, have a general composition as follows:
(salt)xc2x7A2xe2x88x92yM3(X2O7)2
wherein:
A=alkali and alkaline-earth metals
M=di- and trivalent transition metals
X=P, As, Si, Ge
and wherein y is greater than or equal to 0 and less than or equal to 1. Single-crystal structural studies show that these materials exhibit microporous frameworks with the pore size in the range of from about 5.3 to about 12.7 angstroms.
In contrast to organically templated microporous solids, the materials of the present invention allow the space-filling, charge-compensation templates to be removed without destroying the framework of the micropore. The materials have a very stable framework, which can endure extensive heating up to 650xc2x0 C. The materials possess very attractive chemical properties in that ion-exchange and insertion (intercalation) reactions can readily take place at room temperature.